Search results for "Geochemistry"
showing 10 items of 2967 documents
The role of Mediterranean wetlands in climate regulation and greenhouse gases exchanges: from carbon biogeochemistry to European water and nature Dir…
2022
Atesa la seua alta activitat biogeoquímica, els aiguamolls són un dels tipus d'ecosistemes més actius en el cicle global del carboni, amb altes taxes d'intercanvi de carboni i de gasos d'efecte hivernacle (GEH), i, per tant, un gran potencial de regulació climàtica. Una de les parts més importants de la biogeoquímica del carboni als aiguamolls està lligada a les taxes metabòliques, a partir del coneixement de les quals es pot determinar un balanç de carboni associat amb el potencial intercanvi de carboni amb l'atmosfera. La seua capacitat per retindre carboni i mitigar el canvi climàtic, o, per contra, d'alliberar més GEH, i contribuir a l'escalfament global, es determina pel balanç de carb…
Aerosol radiative forcing efficiency in the UV region over southeastern Mediterranean: VELETA2002 campaign
2007
Atmospheric aerosol effects on spectral global UV irradiance were evaluated during the VELETA2002 field campaign between 8 and 19 July 2002 in southeast Spain. In the first stage, seven UV spectroradiometer and six CIMEL Sun photometer measurements were carried out simultaneously, allowing them to be calibrated and intercompared. The mean ratio obtained for the global irradiance between the spectroradiometers, with regards to a reference instrument, ranges from 0.98 up to 1.04 with standard deviations that oscillate between ±0.01 and ±0.17. In particular, the two spectroradiometers used to obtain the aerosol forcing efficiencies have a ratio of 1.000 ± 0.001. The aerosol optical depth (AOD)…
Partial melting of metabasic rocks and the generation of tonalitic–trondhjemitic–granodioritic (TTG) crust in the Archaean: Constraints from phase eq…
2020
Abstract Rocks of tonalitic–trondhjemitic–granodioritic (TTG) composition preserved in Archaean terranes represent fragments of the Earth’s earliest-formed continental crust, and are thought to have formed via partial melting of hydrated metabasalt. The geodynamic environments in which such high-grade metamorphism and anatexis may have occurred in the early Earth is strongly debated. Constraining the pressure ( P ) and temperature ( T ) conditions at which melts of appropriate composition can be derived from protoliths containing plausible mineral assemblages is central to addressing this question. Phase equilibrium modelling has been undertaken for an enriched Archaean tholeiite bulk compo…
Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry
2020
International audience; Magnetite is a ubiquitous oxide in ultramafic and mafic rocks, which is present in a large range of geological and tectonic settings. In the case of high-pressure ultramafic rocks, exhumation timing is commonly constrained by geochronometers in nearby lithologies. The development of the magnetite (U-Th-Sm)/He method (MgHe) has opened new perspectives to refine the exhumation history of such rocks. However no thermal history has been deduced using MgHe data so far. Here we applied MgHe dating to magnetite from an HP-LT alpine ophiolite body (Rocher Blanc) from the Schistes lustres units (Western Alps, France) where part the P-T-t history is constrained to further refi…
Delamination and recycling of Archaean crust caused by gravitational instabilities
2013
The volume of Archaean crust preserved at Earth’s surface today is low. Thermodynamic calculations and geodynamic modelling show that the thick, primary crust that would have formed on a much hotter Archaean Earth was denser than the underlying mantle, and would have therefore been recycled back into the mantle as drips.
SHRIMP ZIRCON AGES AND PETROLOGY OF LOWER CRUSTAL GRANULITE XENOLITHS FROM THE LETSENG-LA-TERAE KIMBERLITE, LESOTHO: FURTHER EVIDENCE FOR A NAMAQUA-N…
2013
Recrystallized zircons extracted from intermediate granulites of the Letseng-la-Terae Diamond Mine in northeastern Lesotho provide evidence that the Tugela Terrane of the Mesoproterozoic high-grade Namaqua-Natal mobile belt may extend ~200 km farther west than previously thought. The rock-forming minerals in the investigated lower crustal granulites contain garnet, clinopyroxene, plagioclase and quartz or garnet, wollastonite, plagioclase and quartz. Calculated values for peak granulite-facies metamorphism are ~13 kbar and ~850°C. Thermal overprint and therein granulite-facies metamorphism occurred during the late Mesoproterozoic and is documented by SHRIMP metamorphic zircon ages of 1018 ±…
Tethyan vs. Cordilleran ophiolites: a reappraisal of distintctive tectono-magmatic features of supra-subduction complexes in relation to the subducti…
2004
Abstract Supra-subduction zone (SSZ) ophiolites deserve special attention because they represent fundamental markers of intraoceanic convergence and generation of new lithosphere above subduction zones. Moreover, owing to their structural characteristics and location in the overriding plate, these complexes are far better represented and preserved than Mid-Ocean-Ridge-Basalt (MORB) ophiolites in orogenic belts. In terms of their structure, tectonics, and magmatic features, SSZ ophiolites may be classified in two main types: (1) “Tethyan complexes” (such as those of the Albanide-Hellenide belt), which mostly consist of complete and extensive volcanic, dyke, plutonic, and mantle sections with…
Reworking of the Tarim Craton by underplating of mantle plume-derived magmas: Evidence from Neoproterozoic granitoids in the Kuluketage area, NW China
2011
Abstract Most Neoproterozoic granitoids in the Kuluketage area, northern Tarim Craton are characterized by strongly depleted HREE abundances and high Sr/Y and (La/Yb) N ratios, showing typical geochemical features of adakitic rocks. Zircon U–Pb dating of three adakitic plutons yielded Neoproterozoic ages (754 ± 4, 790 ± 3 and 798 ± 3 Ma). The adakitic granitoids exhibit low MgO and TiO 2 contents. Their low Cr, Co and Ni abundances, low ɛ Hf ( t ) values (−21 to −11) and high FeO T /MgO ratios (mostly 2.2–2.9) preclude the possibility of being derived from partial melts of delaminated lower crust. The relatively low ɛ Hf ( t ) values and old Hf two-stage model ages ( T DM 2 = 2 . 42 – 3 .0 …
High-Grade Mylonites
2009
High-grade mylonites are formed at temperatures above 650 °C. They are relatively uncommon, probably because their conservation is problematic. Most mylonites formed under these conditions would tend to fully recrystallise which destroys and masks the mylonitic structure. Mylonitic features are only preserved if grain growth is somehow inhibited in the rock, e.g. by its polymineralic nature.
Dynamics of outgassing and plume transport revealed by proximal Unmanned Aerial System (UAS) measurements at Volcán Villarrica, Chile
2019
Volcanic gas emissions are intimately linked to the dynamics of magma ascent and outgassing, and, on geological timescales, constitute an important source of volatiles to the Earth's atmosphere. Measurements of gas composition and flux are therefore critical to both volcano monitoring and to determining the contribution of volcanoes to global geochemical cycles. However, significant gaps remain in our global inventories of volcanic emissions, (particularly for CO2, which requires proximal sampling of a concentrated plume) for those volcanoes where the near‐vent region is hazardous or inaccessible. Unmanned Aerial Systems (UAS) provide a robust and effective solution to proximal sampling of …